This disclosure relates to vehicle headlamp system, and more particularly a headlamp system that employs a high intensity discharge lamp in which three different lighting functions or modes are integrated into a single assembly. Selected aspects of this disclosure may find application in related headlamp arrangements and possibly find application outside of the headlamp art.
Discharge vehicle light sources are known in the art and are conventionally called xenon lamps. These discharge light sources are being used with increasing degree of penetration into the vehicle lighting market because of the advantageous benefits of higher luminous intensity, higher brightness, as well as lower power consumption as a result of the extremely high efficacy of the discharge lamps.
One downside of the xenon lamps is associated with the high cost of the lighting system. By way of the lighting system, a lighting system according to this disclosure includes the lamp, the headlamp unit (reflector, lenses, etc.), and the driving electronics of the lamp. The increased cost associated with discharge light sources has limited the penetration of these types of lamps into the mid-priced and low-priced vehicle classes. In part, an effective discharge headlamp assembly must be capable of performing multiple tasks or operating in multiple modes with a single unit. Some solutions provide for separate light sources between low beam and high beam applications or functions. More recently, so-called bi-xenon headlamp units perform low beam and high beam functions by applying a single xenon lamp system and mechanically switching the headlamp system architecture so that a change from a cut-off free high beam operation mode to a low beam operation mode with beam cut-off occurs.
U.S. Pat. No. 7,029,155 teaches a motor vehicle headlight that enables at least two functions to be obtained with a single structure, namely a daytime running light (DRL) function/mode and an infrared beam function/mode. Particularly, a reflector receives light from a high intensity discharge light source and directs the light in a beam where a filter is selectively positioned in the light path or light beam. The filter ensures sufficiently high absorption and spreading of the light beam. Thus, the headlight assembly operates in a first mode without the filter, and then operates in a second mode when the filter is situated in the light path. In a third mode of operation, an infrared filter is selectively disposed in the light path so that only an infrared beam is delivered.
In other instances, a separate incandescent light source is used to provide high beam operation while the high intensity discharge operation is provided for low beam operation. Alternately, the incandescent light source has been proposed as an auxiliary light source and located either inside or outside the headlamp unit to perform DRL operation mode. It will be appreciated that the use of a separate incandescent light source, whether incorporated within the headlamp assembly, or externally thereto, still adds additional cost to the lighting system. The additional light source also constrains the geometry and design of the headlamp, increases the headlamp wiring cost, and limits the freedom of design. Thus, although a bi-xenon discharge headlamp system may provide part of a solution of a single headlamp system between high beam and low beam modes of operation, discharge lamps, especially high intensity discharge lamps such as xenon automotive lamps, are difficult to dim. Dimming to power levels below sixty to seventy percent (60-70%) can potentially extinguish the arc at power levels well below the design value. Further, dimming to DRL operation mode where much less light is required further exacerbates the design issue of generating low light intensity in the headlamp that is still sufficient to be detectable at the required safety level by an oncoming car driver for the DRL operation mode, while simultaneously using the same headlamp system to achieve both low beam and high beam operation modes.
Thus, a need exists for a three-mode dimmable headlamp system that meets these needs and others in an efficient, effective, and cost competitive manner.